public class Main {
    public static void main(String[] args) {
        System.out.println("Hello world!");
    }
}


class Solution {
    public String replaceSpace(String s) {
        StringBuilder stringBuilder = new StringBuilder();
        for (int i = 0; i < s.length(); i++) {
            stringBuilder.append(s.charAt(i) == ' ' ? "%20" : s.charAt(i));
        }
        return stringBuilder.toString();
    }
}